Keywords: fMRI Acquisition, fMRI, z-shim
Motivation: Z-shimming ameliorates through-slice dephasing in T2*-weighted functional neuroimaging but, surprisingly, a linear fit to the field in slice direction may not provide z-shim settings yielding the maximum signal.
Goal(s): To demonstrate that optimum z-shim settings should be obtained from a reference acquisition stepping through a range of z-shims at the desired echo time.
Approach: Numerical simulations of the MR signal were performed for different through-slice field distributions, echo times, and z-shims.
Results: Z-shims derived from the linear fit minimize the dephasing but this is not equivalent to maximizing the signal. Furthermore, optimum z-shim settings may depend on the echo time.
Impact: The results could help to optimize z-shim settings in T2*-weighted acquisitions used for BOLD-based functional neuroimaging by using a reference acquisition stepping through a range of z-shims at the desired echo time rather than a fit to the field distribution.
How to access this content:
For one year after publication, abstracts and videos are only open to registrants of this annual meeting. Registrants should use their existing login information. Non-registrant access can be purchased via the ISMRM E-Library.
After one year, current ISMRM & ISMRT members get free access to both the abstracts and videos. Non-members and non-registrants must purchase access via the ISMRM E-Library.
After two years, the meeting proceedings (abstracts) are opened to the public and require no login information. Videos remain behind password for access by members, registrants and E-Library customers.
Keywords